The BGS Lexicon of Named Rock Units — Result Details

The formation comprises a sheet of interbedded gravels, sands, silts and clays. The gravels are dominated by flint (up to c.80%) and by quartz and quartzite (up to c.60%), with far-travelled minor lithogies including Carboniferous chert, Rhaxella chert, Greensand chert, Spilsby Sandstone and felsic volcanic rocks from North Wales. The deposits are interpreted as estuarine and near-shore marine.

Definition of Lower Boundary:

Disconformable on the Norwich Crag, from which it can be distinguished by the generally coarser and less well sorted nature of the sediments and by the presence of significant quantities of quartz, quartzite and far-travelled clasts in the gravels. The formation cuts down through the Norwich Crag northwards and comes to rest on Chalk Group bedrock in north Norfolk.

Definition of Upper Boundary:

Widely overlain by Mid Pleistocene glacial deposits, less widely by deposits of the Bytham Valley Subgroup and the Cromer Forest-bed Formation. It is distinguished from the latter units by sedimenrary, etc, features related to its marine origin.

Thickness:

c.20m

Geographical Limits:

Restricted to eastern Norfolk and northeastern Suffolk, at least as far south as Halesworth.

Moorlock, B S P, Hamblin, R J O, Booth, S J and Woods, M A. 2002. Geology of the Mundesley and North Walsham district - a brief explanation of the geological map. Sheet explanation of the British Geological Survey. 1:50 000 Series Sheets 132 and 148 Mundesley and North Walsham (England and Wales).

Wood, S V. 1866. On the structure of the Red Crag. Quarterly Journal of the Geological Society of London, Vol.22, 538-552.

Wood, S V and Harmer, F W. 1872. An outline of the geology of the upper Tertiaries of East Anglia. Monograph of the Palaeontological Society, Vol.25, ii-xxxi.

Reid, C. 1882. The geology of the country around Cromer. Memoir of the Geological Survey of Great Britain.